the effect of prolonged culture of chromosomally abnormal human embryos on the rate of diploid cells

background: a decrease in aneuploidy rate following a prolonged co-culture of human blastocysts has been reported. as co-culture is not routinely used in assisted reproductive technology, the present study aimed to evaluate the effect of the prolonged single culture on the rate of diploid cells in human embryos with aneuploidies. materials and methods: in this cohort study, we used fluorescence in situ hybridization (fish) to reanalyze surplus blastocysts undergoing preimplantation genetic diagnosis (pgd) on day 3 postfertilization. they were randomly studied on days 6 or 7 following fertilization. results: of the 30 analyzed blastocysts, mosaicism was observed in 26(86.6%), while 2(6.7%) were diploid, and 2(6.7%) were triploid. of those with mosaicism, 23(88.5%) were determined to be diploid-aneuploid and 3(11.5%) were aneuploid mosaic. the total frequency of embryos with more than 50% diploid cells was 33.3% that was lower on day 7 in comparison with the related value on day 6 (p<0.05); however, there were no differences when the embryos were classified according to maternal age, blastocyst developmental stage, total cell number on day 3, and embryo quality. conclusion: although mosaicism is frequently observed in blastocysts, the prolonged single culture of blastocysts does not seem to increase the rate of normal cells.